2017 27' Flying Cloud
2016 Interstate Grand Tour Ext
Altoona
, Florida
Join Date: Aug 2005
Posts: 1,644
454 diesel effect
Ok you big block nuts, I have a 1990 classic with a carburated 454 and she runs strong but lately she runs a high idle, diesels for a min or two, and loudly backfires like a gun shot. Last time I opened the gas filler cap, I noticed pressure released?? Any ideas?
Check your timing, see if the distributor clamp has become loose. Just try to turn it and if it moves you need to tighten the clamp after timing it. Also check for vaccuum leaks which would account for the high idle too.
My ’73 GMC with a 454 had a solenoid on the throttle that held it open to idle speed. When you shut off the ignition, it would drop closing the blades. It was specifically to prevent dieseling after shut down. Does your have anything like that? Just a thought.
2009 27' FB Flying Cloud
1982 31' International
1991 35' Airstream 350
Jay
, Oklahoma
Join Date: Oct 2006
Posts: 1,712
I agree with timing advanced or more likely, a cracked vaccuum line or fitting somewhere. A little WD40 sprayed along the lines will cause the idle to increase at the leaking point.
Good Luck!
__________________
Jeff & Cindy
'09 27FB Flying Cloud;'82 31 International
'91 350 LE MH; '21 Interstate 24GT
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